"The Department of Justice takes seriously reports of any data breach, particularly those involving personally identifiable or financial information, and looks into allegations that are brought to its attention,'' Holder told the Senate Judiciary Committee.

"While we generally do not discuss specific matters under investigation, I can confirm the department is investigating the breach involving the U.S. retailer, Target. And we are committed to working to find not only the perpetrators of these sorts of data breaches – but also any individuals and groups who exploit that data via credit card fraud.''

During the crucial holiday season, the retailer said that cyberthieves hacked 40 million debit and credit card accounts, stealing encrypted PIN data, customer names, credit and debit card numbers, card expiration dates and the embedded code on the magnetic strip on the back of cards used at Target between Nov. 27 and Dec. 15.

In January, the retailer revealed the hackers also stole additional information — including names, home addresses, email addresses and phone numbers — of about 70 million people.

The retailer says it is working with federal officials in the investigation of the data breach.

"I know that it is frustrating for our guests to learn that this information was taken, and we are truly sorry they are having to endure this," Target CEO Gregg Steinhafel said in a recent press release.